login
Numbers k such that k concatenated with k+2 is a prime.
4

%I #13 Jul 28 2021 04:19:48

%S 1,7,9,27,37,45,49,51,55,61,69,75,105,109,115,117,121,151,159,181,187,

%T 195,201,211,217,225,247,271,277,285,289,291,301,309,319,321,331,337,

%U 339,357,361,367,381,391,399,405,417,421,427,429,435,439

%N Numbers k such that k concatenated with k+2 is a prime.

%H Robert Israel, <a href="/A032617/b032617.txt">Table of n, a(n) for n = 1..10000</a>

%p filter:= n -> isprime(n*(10^(1+ilog10(n+2))+1)+2):

%p select(filter, [seq(i,i=1..1000,2)]); # _Robert Israel_, Nov 14 2019

%Y Cf. A032607.

%K nonn,base

%O 1,2

%A _Patrick De Geest_, May 15 1998